A group of monkeys was irradiated 250 rads twice weekly for 2 weeks using Cobalt 60 as a radiation source. The animals were fed a high sugar diet. Considerable caries developed around the necks of teeth after 2 months. There was considerable overgrowth by S. mutans in the plaque as revealed by cultural and fluorescent technics. There is considerable need to develop an effective and rapid method of screening substances with cariostatic potential. Primates appear to be a particularly good model. However, caries usually take an inordinately long time to develop. If a way could be developed to enhance the carious process in primates the way would be open to realize the potential of the primate model more effectively. Thus, compounds which protect against caries in such a model could be investigated in humans with confidence.